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Abstract:

The present invention is directed to a new more environmentally friendly
method for the recovery of uranium from pregnant liquor solutions that
comprise high levels of chloride by using an amino phosphonic
functionalized resin.

Claims:

1) A method for the recovery of uranium from a pregnant liquor solution
comprising: i) providing an amino phosphonic functionalized resin; ii)
providing a pregnant liquor solution comprising chloride and uranium;
iii) passing the pregnant liquor solution over the amino phosphonic
functionalized resin to separate the uranium from the pregnant liquor
solution; and iv) eluting the uranium wherein the chloride is present in
an amount from 5 to 80 g/L.

2) The method of claim 1 wherein the pregnant liquor solution has a pH of
from 0 to 4.

5) The method of claim 1 wherein the amino phosphonic functionalized
resin is in sodium form.

6) The method of claim 1 further wherein at least 10% of the amount of
uranium from the pregnant liquor solution is recovered.

7) The method of claim 1 further wherein up to 25% of the amount of
uranium from the pregnant liquor solution is recovered.

Description:

[0001] The present invention is directed to a new more environmentally
friendly method for the recovery of uranium from acid leach pregnant
liquor solutions that comprise high levels of chloride by using an amino
phosphonic functionalized resin.

[0002] Numerous minerals are present in subsurface earth formations in
very small quantities which make their recovery extremely difficult.
However, in most instances, these minerals are also extremely valuable,
thereby justifying efforts to recover the same. An example of one such
mineral is uranium. However, numerous other valuable minerals, such as
copper, nickel, molybdenum, rhenium, silver, selenium, vanadium, thorium,
gold, rare earth metals, etc., are also present in small quantities in
some subsurface formations, alone and quite often associated with
uranium. Consequently, the recovery of such minerals is fraught with
essentially the same problems as the recovery of uranium and, in general,
the same techniques for recovering uranium can also be utilized to
recover such other mineral values, whether associated with uranium or
occurring alone. Therefore, a discussion of the recovery of uranium will
be appropriate for all such minerals.

[0003] Uranium occurs in a wide variety of subterranean strata such as
granites and granitic deposits, pegmatites and pegmatite dikes and veins,
and sedimentary strata such as sandstones, unconsolidated sands,
limestones, etc. However, very few subterranean deposits have a high
concentration of uranium. For example, most uranium-containing deposits
contain from about 0.01 to 1 weight percent uranium, expressed as
U3O8 as is conventional practice in the art. Few ores contain
more than about 1 percent uranium and deposits containing below about 0.1
percent uranium are considered so poor as to be currently uneconomical to
recover unless other mineral values, such as vanadium, gold and the like,
can be simultaneously recovered.

[0004] There are several known techniques for extracting uranium values
from uranium-containing materials. One common technique is roasting of
the ore, usually in the presence of a combustion supporting gas, such as
air or oxygen, and recovering the uranium from the resultant ash.
However, the present invention is directed to the extraction of uranium
values by the utilization of aqueous Teaching solutions. There are two
common leaching techniques (or lixiviation techniques) for recovering
uranium values, which depend primarily upon the accessibility and size of
the subterranean deposit. To the extent that the deposit containing the
uranium is accessible by conventional mining means and is of sufficient
size to economically justify conventional mining, the ore is mined,
ground to increase the contact area between the uranium values in the ore
and the leach solution, usually less than about 14 mesh but in Some
cases, such as limestones, to nominally less than 325 mesh, and contacted
with an aqueous leach solution for a time sufficient to obtain maximum
extraction of the uranium values. On the other hand, where the
uranium-containing deposit is inaccessible or is too small to justify
conventional mining, the aqueous leach solution is injected into the
subsurface formation through at least one injection well penetrating the
deposit, maintained. in contact with the uranium-containing deposit for a
time sufficient to extract the uranium values and the leach solution
containing the uranium, usually referred to as a "pregnant" liquor
solution (PLS), is produced through at least one production Well
penetrating the deposit. It is this latter in-situ leaching of subsurface
formations to which the present invention is directed.

[0005] The most common aqueous leach solutions are either aqueous acidic
solutions, such as sulfuric acid solutions, or aqueous alkaline
solutions, such as sodium carbonate and/or bicarbonate.

[0006] Aqueous acidic solutions are normally quite effective in the
extraction of uranium values. However, aqueous acidic solutions generally
cannot be utilized to extract uranium values from ore or in-situ from
deposits containing high concentrations of acid-consuming gentle, such as
limestone. While some uranium in its hexavalent state is present in ores
and subterranean deposits, the vast majority of the uranium is present in
its valence states lower than the hexavalent state. For example, uranium
minerals are generally present m the form of uraninite, a natural oxide
of uranium in a variety of forms such as UO2, UO3,
UO.U2O3 and mixed U3O8(UO2.2UO3), the most
prevalent variety of Which is pitchblende containing about 55 to 75
percent of uranium as UO2 and up to about 30 percent uranium as
UO3. Other forms in which uranium minerals are found include
coffinite, carnotite, a hydrated vanadate of uranium and potassium having
the formula K2(UO2)2(VO4)2.3H2O, and
uranites which are mineral phosphates of uranium with copper or calcium,
for example, uranite lime having the general formula
CaO.2UO3.P2O5.8H2O, Consequently, in order to extract
uranium values from subsurface formations with aqueous acidic leach
solutions, it is necessary to oxidize the lower valence states of uranium
to the soluble, hexavalent slate.

[0007] Combinations of acids and oxidants which have been suggested by the
prior art include nitric acid, hydrochloric acid or sulfuric acid,
particularly sulfuric acid, in combination with air, oxygen, sodium
chlorate, potassium permangante, hydrogen peroxide and magnesium
perchlorate and dioxide, as oxidants. However, the present invention is
directed to the use of sulfuric acid leach solutions containing
appropriate oxidants and other additives, such as catalysts.

[0008] There are two commonly used methods for the recovery of uranium
from pregnant liquor solution (PLS). One technique, solvent extraction,
employs the use of a non aqueous solvent to selectively extract uranium
from the PLS.

[0009] The second method involves ion exchange technology. Strong and weak
base anion exchange resins are commonly used. This ion exchange method
has become the more preferred method of uranium recovery in various
regions of the world because of its environmental benefits as well as its
safety benefits. Flammable toxic solvents need not be used for the
present method as compared to the solvent extraction method where harmful
chemicals are employed.

[0010] Additionally it has been discovered that in environments where
there is a relatively high concentration of chloride, i.e. greater than 5
g/L, based on the composition of the PLS fouling of the ion exchange
resin occurs. This fouling results in a decreased loading capacity of the
resin. U.S. Pat. No. 4,599,221 uses an amino phosphonic functionalized
resin to recover uranium from phosphoric acid; however a need exists for
a method to recover uranium from acid leach in high chloride
environments. Recovery of uranium from phosphoric acid is a different
process from the acid leach process because there are competing ions,
such as chloride, in and acid leach solution that can foul any recovery
media. The phosphoric acid process does not have such. Additionally, the
levels of uranium in a phosphoric acid process are relatively low, i.e.
less than 300 ppm. In acid leach, the batting capacity of uranium must be
much greater as the levels of uranium in acid leach liquors can be
present in up to 2000 mg/L (or ppm) It is known that for the same
concentration of U in the PLS, the operating capacity is much greater in
acid leach liquor than in phosphoric acid liquor. Therefore one of skill
in the an would not typically apply the same techniques from the recovery
of metals from phosphoric acid to acid leach.

[0011] The present invention solves these problems of the art by proving
an amino phosphonic functionalized resin useful for the recovery of
uranium that does not foul in chloride environments of greater than 5
g/L.

[0012] The present invention provides a method for the recovery of uranium
from a pregnant liquor solution comprising:

[0015] iii) passing the pregnant liquor solution over the amino phosphonic
functionalized resin to separate the uranium from the pregnant liquor
solution; and

[0016] iv) eluting the uranium

wherein the chloride is present in an amount from 5 to 80 g/L.

[0017]FIG. 1 shows a graph of the results of dynamic loading versus flow
rate in the Example; and

[0018] FIG. 2 shows a graph of the results of uranium concentration versus
pH in the Example.

[0019] As used herein the term amino phosphonic functionalized resin is
meant to include either an amino phosphonic resin or an amino
hydrophosphonic functionalized resins.

[0020] In the present invention the resin is a styrene polymer resin
having active amino phosphonic functional groups linked to the polymer
matrix. The term "styrene polymer" indicates a copolymer polymerized from
a vinyl monomer or mixture of vinyl monomers containing styrene monomer
and/or at least one crosslinker, wherein the combined weight of styrene
and cross linkers is at least 50 weight percent of the total monomer
weight. The level of cross linking ranges from 4 to 10%. All percentages
herein are weight percentages.

[0022] The structure of the polymer can be either gel or macroporous
(macroreticular). The term "gel" or "gellular" resin applies to a resin
which was synthesized from a very low porosity (0 to 0.1 cm3/g),
small average pore size (0 to 17 Å) and low B.E.T. surface area (0 to
10 m2/g) copolymer. The term "macroreticular" (or MR) resin is
applied to a resin which is synthesized from a high mesoporous copolymer
with higher surface area than the gel resins. The total porosity of the
MR resins is between 0.1 and 0.7 cm3/g, average pore size between 17
and 500 Å and B.E.T. surface area between 10 and 200 m2/g. The
resin is in acid form.

[0023] The resin is used to treat an acid leach pregnant liquor solution
(PLS). The PLS of the present invention comprises uranium and chloride.
Uranium is primarily present in the form of U3O8; although
other commonly known forms and isotopes of uranium may be present.

[0024] As used herein, the term uranium refers to all forms and isotopes
of uranium. Uranium is present in the PLS in an amount from 25 to 2000
mg/L, preferably from 50 to 1500 mg/L, and further preferably from 100 to
1000 mg/L. Chloride ion and chloride complexes together as "chloride" is
present in the PLS in an amount from 5 to 80 g/L and preferably form 7 to
70 g/L and further preferably from 15 to 50 g/L. The PLS of the present
invention may optionally contain a variety of other components. Such
components include but are not limited to: iron, sulfuric acid, sodium,
calcium, potassium, copper, phosphorus, and aluminum. The pH of the PLS
is acidic and ranges from 0 to 4. Furthermore, the PLS may be obtained
from any method commonly known to those of skill in the art including but
not limited to in situ leach, heap, leach, resin in pulp, and in situ
recovery.

[0025] Uranium is separated from the PLS by passing the PLS over the amino
phosphonic functionalized resin. Techniques commonly used in the art to
separate the uranium from the PLS may be applied. Such techniques include
but are not limited to fixed bed, co-current or countercurrent fluidized
bed. The process may be batch or continuous. Typically the flow rate
within the column or packed bed system is from 0.5 to 50 BV/h, preferably
1 to 50 BV/h, more preferably 2 to 45 BV/h.

[0026] The amino phosphonic functionalized resin retains the uranium from
the PLS and the uranium is then recovered by elution. Methods of elution
used by those of ordinary skill in the art are used herein. In one
instance, for example, the uranium loaded resin may be treated with a
solution of ammonia or ammonia hydroxide. Afterwards, the resin is eluted
with a solution of sodium carbonate. The uranium is then recovered from
solution by known separations techniques, such as for example
precipitation. It is beneficially found that the at least 10% of the
uranium found in the original PLS may be recovered. Within the pH range
of 0 to 4 of the PLS, uranium recovery levels of up to 25% may be
achieved.

[0030] AMBERLITE® IRC 747, is a registered trademark of Rohm and Haas
Company, a wholly owned subsidiary of The Dow Chemical Company. The resin
is in sodium form having a polystyrenic matrix, crosslinked with divinyl
benzene and containing aminophosphonic functional groups. Note The resin
was converted in its appropriate ionic form (i.e: acidic form) before
carrying out the experiments.

[0035] All experiments were carried out at 25° C. A sample was
taken every 10 bed volumes for uranium analysis. The leakage curves were
obtained as shown in FIG. 1.

[0036]FIG. 1 shows that the resin loading is not affected when the
chloride concentration increases from 0 to 20 g/L.

[0037] The uranium loading increases when the flow rate decreases. The
operating capacity is around 15 g/LR (expressed as U) at a flow rate
equates to 5 BV/h and around 21 g/LR (expressed as U--g/LR stands for
"gram per liter of resin in its ionic form considered"--i.e: acidic form)
when the flow rate equates 2.5 BV/h.

[0038] Elution

[0039] The loaded resins were treated with 2 bed volumes of a solution of
ammonia hydroxide at a concentration of 1 mol/L (1N). Afterwards, the
resins were eluted with a solution of sodium carbonate at a concentration
of 1 N.

[0040] The totality of uranium loaded was eluted within 7 bed volumes of
sodium carbonate solution.

[0041] Experiment 5: Several solutions containing 200 mg/L of uranium
(expressed as U), 24 g/L of sulfate, 0 g/L of chloride were prepared.
Each solution was adjusted a different pH level. A sample of resin was
put in contact with each solution. The ratio of 1 part resin to 50 parts
of solution was kept constant in order to avoid any external
perturbation. After shaking for 8 hours, the analysis of the uranium
residual in the supernatant was analyzed and the resin loading
determined. FIG. 2 indicates that the optimum loading is obtained when
the pH equates 4. Above pH 4, precipitation of Uranium was observed. It
was also observed that the loading was very good at pH 0. The results are
shown in FIG. 2.